Optical raster-to-line converter

ABSTRACT

A two-dimensional matrix array of light beams is translated into a linear array having the same number of spots. This is accomplished by an optical converter that comprises a cylindrical lenslet plate crossed, not quite orthogonally, with a single cylindrical lens. Each column of the matrix array of light beams is imaged by the converter to form a segment of the final line array.

United States Feldman 1 May 22, 1973 [54] OPTICAL RASTER-TO-LINE [56]Relerences Cited CONVERTER UNITED STATES PATENTS [751 n splinlfielldi2,02l,l62 11/1935 Walton ..350/1s1 ux [73] Assignee: Bell TelephoneLaboratories, lncorpanned, Murray Hill Primary Examiner-John K. CorbmAtt0rneyW. L. Keefauner [22] Filed: Nov. 9, I971 211 App]. No.: 196,994[571 ABSTRACT A two-dimensional matrix array of light beams is 52 US.Cl. .350 190 350/167 350/181 "anslmd a near may having the Same "umber[5 1 Int Cl G02; 3/06 G62) 27/00 of spots. This is accomplished by anoptical converter [58] i 3 18] 213 that comprises a cylindrical lensletplate crossed, not 350/150 5 quite orthogonally, with a singlecylindrical lens. Each column of the matrix array of light beams isimaged by the converter to form a segment of the final line array.

6 Claims, 6 Drawing Figures ODU 43's xsso-t's,

1 OPTICAL RASTER-TO-LINE CONVERTER This invention relates to theselective translation of light beams and more particularly to anapparatus for converting a two-dimensional matrix array of light beamsinto a linear array of spots.

BACKGROUND OF THE INVENTION often exceeds substantially the capacity ofpresently available acousto-optic deflectors.

It is known that the number of resolvable light spots obtainable byacousto-optic techniques can be increased by cascading two orthogonallydisposed acousto-optic deflectors. However, the beams generated by suchan arrangement form a rectangular matrix array or raster. Accordingly,in pursuing this particular approach, some form of converter is neededfor translating the raster to a line array of spots.

Such raster-to-line converters are known. For example, in a copendingapplication of M. Feldman and J. P. Griffin, Ser. No. 39,583, filed May22, 1970, now U.S. Pat. No. 3,627,405 there is described a series ofmirrors arranged to form a staircase which converts a rectangular matrixof light beams to a close approximation of a linear array of spots.Other specific schemes, utilizing, for example, optical fibers, mirrors,or multifaceted prisms, have been suggested for carrying out the notedconversion.

SUMMARY OF THE INVENTION An object of the present invention is animproved optical converter.

More specifically, an object of this invention is an improved opticalraster-to-line converter that is characterized by simplicity,reliability, low cost and ease of alignment.

Briefly, these and other objects of the present invention are realizedin a specific illustrative embodiment thereof that comprises amulti-element cylindrical lenslet plate crossed, not quite orthogonally,with a'single cylindrical lens. Such an arrangement is adapted totranslate a two-dimensional matrix array of light beams into a lineararray having the same number of spots. Each column of the matrix arrayof light beams is directed to a different element of the lenslet plateand is imaged to form a segment of the final line array. In particular,if each column of n light beams of an m-by-n input array is directed tofall along the main axis of a different one of m cylindrical lenses ofthe lenslet plate, the n beams of each input column will be imaged intoa row of n smaller spots along a horizontal line parallel to the axis ofthe single cylindrical lens.

BRIEF DESCRIPTION OF THE DRAWING FIG. I shows a prior art system forgenerating a twodimensional raster of light beams;

FIG. 2 depicts a particular tilted raster of light beams of the typeadapted to be converted to a line array by an embodiment of theprinciples of the present invention;

FIG. 3 is a top cross-sectional view of a specific illustrativeconverter made inaccordance with the principles of this invention;

FIG. 4 is a side view of the FIG. 3 converter;

FIG. 5 is a front view of the FIG. 3 converter with the FIG. 2 rastersuperimposed thereon; and

FIG. 6 shows the line array which is formed by the FIG. 3 converter inresponse to having the FIG. 2 raster directed thereat.

DETAILED DESCRIPTION The prior art system shown in FIG. I is adapted todeflect a light beam provided by source 10 to successive ones of aplurality of target areas in output plane 12. The target areas in plane12 are arranged to form a two-dimensional array or raster having pluralrows and columns.

The source 10 of FIG. 1 comprises, for example, an argon ion laser whichsupplies light at 4,880 A. Illustratively, the output of the source 10is a collimated light beam with a circular cross-section which istypical of a laser operating in the TEM transverse mode. Other types ofsources, such as, for example, expanded or contracted laser beams,higher-order laser beams, collimated and/or filtered arc discharges orother light sources, also may be employed to provide a light beam to bedeflected by the depicted system.

The relatively small diameter of the light beam supplied by the source10 of FIG. 1 is increased by a conventional beam-expanding telescope 14before the beam is applied to a conventional vertical deflector 16. Thedeflector 16 may, for example, be of the acoustooptic type. (Thephenomenon underlying the mode of operation of acoustooptic deflectorsis described by E. I. Gordon in the Proceedings of the IEEE, October,1966, pages l,39l-l,40l.) Thereafter, the vertically deflected beampropagates through a prism 18 which further enlarges its diameter beforethe beam enters a conventional horizontal deflector 20 which also may beof the acousto-optic type. In this way, relatively high horizontalresolution is obtained. The cascaded deflectors 16 and 20, one rotatedapproximately with respect to the other, constitute a conventional x-ydeflection arrangement.

Another prism 22 (FIG. 1) disposed in the path of the propagating lightis effective to increase the angular deflection of the beam. An imaginglens 24 and a lens 26 serve to project the deflected beam onto theoutput plane 12. Illustratively, the raster formed thereby ischaracterized by a large aspect ratio (i.e., a large widthto-heightratio). This characteristic is achieved as a result of the action of theprism 22.

Prior art systems, whether they are of the particula type shown in FIG.1 or variations thereof, are generally designed to deflect an incidentlight beam to a rectangular matrix array of target areas. In accordancewith the principles of the present invention, however, such a system isspecifically adapted to produce a two dimensional array of light spotswhose columns are slightly tilted from the vertical. This tilted effectis achieved, for example, simply by successively increasing the amountof horizontal deflection during the time of each vertical sweep. Anillustrative such tilted array, comprising 16 target areas 30 through 45disposed in output plane 12, is represented in FIG. 2. (The significanceof the dashed-line circle 46 will be discussed later below.) In FIG. 2,the columnar axes are each parallel to each other and form an angle withvertical line 48.

The particular mechanism employed to form a tilted raster of the generaltype represented in FIG. 2 is unimportant. However formed, such a rasteris adapted to be converted by an embodiment made in accordance with thisinvention into a line array of target areas.

The specific illustrative converter shown in FIGS. 3 and 4 includes amulti-element lenslet plate 50. An optical raster to be converted isdirected to impinge on the left-hand or input face of the plate 50. Eachelement of the plate is a cylindrical lens having a focal length f. Suchplates, made, for example, of plastic, are commercially available.Spaced apart from the plate 50 and confocal with it is a conventionalhorizontal cylindrical lens 52. Illustratively, the element 52 is asingle horizontal plano-convex cylindrical lens. To provide physicalclearance between the elements 50 and 52, the focal length of the lens52 is assumed to be approximately 0.9 f. A utilization device 54, forexample a screen, is positioned in alignment with the elements 50 and52.

FIG. 5, which shows a front view of the converter of FIGS. 3 and 4,indicates the relative alignment on the input face of the lenslet plate50 of an optical raster to be converted. The depicted raster isidentical to that illustrated in FIG. 2.

As indicated in FIG. 5, the main longitudinal axis of each one of thecylindrical lenses formed on the plate 50 is tilted at an angle 0 withrespect to vertical line 58. This angle is the same as theaforementioned angle of tilt of the respective columns of the inputraster. Moreover, the n light spots in each different one of the m inputcolumns are advantageously centered on a corresponding one of the tiltedmain axes of the lenses on the plate 50.

For illustrative purposes, the target areas in each column of the rastershown in FIGS. 2 and 5 are depicted as being tangent to each other. Eachinput column of tangent light beams, when projected onto the outputdevice 54 (FIGS. 3 and 4), constitutes a segment of the final linearray. For tangent input beams, the corresponding line segment alsoconsists of tangent beams. (But as discussed below, the beams or spotsin the line array are reduced in size relative to the input beams.)Thus, for example, the input column comprising beams 30 through 33 (FIG.5) is imaged onto the device'54 to form four output spots that aretangent to each other along the leftmost portion of a horizontal outputline. From left to right, looking at the device 54 from the lens 52, thespots that comprise this leftmost portion are derived respectively fromthe input beams designated 30, 31, 32 and 33.

For many applications of practical interest, it is desired that all thelight spots in the final array provided by a converter made inaccordance with this invention be equally spaced along a horizontalline. To achieve this result with the particular input rasterrepresented in FIG. 5, it is accordingly necessary that the various linesegments corresponding to the respective columns of the input raster beimaged on the output device 54 tangent to each other In other words,referring to FIG. 5, it is desired that the rightmost beam 33 of theleftmost portion of the final line array be tangent to the beam 34.Similarly, it is desired that the beams 37 and 38, and 41 and 42, berespectively tangent to each other in the line array. If this isachieved, the final array comprises sixteen tangent reduced-size spots30 through 45 arranged in a line from left to right on the output device54, as depicted in FIG. 6.

It is a simple matter to design the format of the particular inputraster shown in FIGS. 2 and 5 to insure that the segments of the finalline array will be tangent to each other. This is accomplished byassuming for design purposes only that the n beams 30 through 33 in theleftmost input column of the raster include another in-line target area,represented by the dashed-line circle 46. The axis along which the areas30 through 33 and 46 lie is then tilted until the bottom beam 34 in thenext parallel input column lies directly (i.e., vertically) under thearea 46. If this specific angle of tilt is established for each of theinput columns, the corresponding line segments on the device 54 will beexactly tangent to each other. In this way, a two-dimensional array oftangent input beams is imaged to form a line of tangent beams. If theinput beams are resolved, their reduced images on the device 54 are alsoresolved.

The described converter exhibits an in-line characteristic in that thewidth W of the final line array (see FIG. 6) is the same as the width W(FIG. 5) of the incident raster and in addition is located directlydownstream from the input array.

As indicated above, the spots included in the output line array arereduced in size relative to the beams in the input raster. Morespecifically, the reduction may be expressed approximately as d sin 0,where 0 is defined above and d is the diameter of a beam in the inputarray.

Moreover, if the beams in the input raster are spaced apart (nottangent), the spacing between adjacentones of their converted images inthe final line array will be reduced approximately by the factor sin 6.

A practical advantage of the aforedescribed converter is that thealignment of the output optical elements is not critical. This arisesfrom the fact that the final image produced by the arrangement is formedrelatively close to the elements 50 and 52.

Alignment of the input optical elements included in the overall systemis also relatively noncritical. This is so because the cylindricallenses included therein demagnify the images. As a result, inputalignment is done on an appreciably larger scale than the spot size ofthe final line array.

In order to reduce aberrations and minimize diffrac+ tion-spreadingeffects, it is advantageous in some applications to use an ellipticallyshaped beam to form the input raster to be applied to a converter of thetype described herein. If elliptically shaped incident beams are used,the images formed on the output device 54 are ellipses of the sameeccentricity rotated by 11/2 0. No loss in resolution results from theuse of such beams. Moreover, if the incident elliptically shaped beamsare tangent, the imaged ellipses in the final line array are tangentalso.

The number of columns in a raster to be applied to a converter made inaccordance with this invention is limited by the capacity of thehorizontal deflector included in the x y deflection system. The numberof spots per column is limited by the capacity of the vertical deflectorand also by diffraction and aberrations in the single cylindrical lens52. These aberrations can be minimized by grinding the lens 52 to forman acylindrical surface, thereby to provide more accurate off-axisfocusing. Alternatively, a compound cylindrical lens or a parabolicmirror can be used in place of the element 52 to provide better focusingand also to demagnify the height of the spots in the final line array.

It is to be understood that the above-described arrangements are onlyillustrative of the principles of the present invention. In accordancewith these principles, numerous other configurations may be devised bythose skilled in the art without departing from the spirit and scope ofthis invention.

I claim:

1. An optical arrangement for reordering a matrix array of rows andcolumns of light spots into a corresponding linear array of light spots,said arrangement comprising:

a light beam directed to any one of a first plurality of target areasarranged in said matrix array of rows and columns, said columns beingaligned at a predetermined angle other than the perpendicular withrespect to said rows; and

means, interposed in the path of said beam and following said matrixarray, for redirecting said beam from any given one of said first targetareas to a corresponding one of an equal number of second nonoverlappingtarget areas disposed in a linear array, said redirecting meanscomprising plural cylindrical lenses, each of said lenses being alignedparallel with a different column of said matrix array and beingconfigured to reduce the images of the target areas in the column in adirection perpendicular to said column, and cylindrical focusing lenspositioned in the path of said beam between said plural cylindricallenses and said linear array of second target areas, said focusing lensbeing aligned parallel with respect to said rows of first target areasto reduce the dimensions in a direction perpendicular to said rows ofeach column of the images of said second target areas and in cooperationwith said plural cylindrical lenses to project said images into saidlinear array of second target areas.

2. The arrangement in accordance with claim 1 in 6 which said lineararray is aligned parallel with the rows of said matrix, and

said cylindrical focusing lens and said plural cylindrical lenses areconfocal with respect to said second target areas.

3. The arrangement in accordance with claim 2 in which said first targetareas have a substantially round geometry, and

said second target areas and the images projected onto said secondtarget areas of said linear array have a substantially round geometry,said images and said second target areas having a diameter reduced byapproximately the factor sin 6 with respect to the diameter of saidfirst target areas.

4. The arrangement in accordance with claim 3 in which said first targetareas are tangential to one another only at points along lines parallelwith said rows and columns and passing through the geometric centers ofsuch target areas, and

said second target areas are tangential to one another only at pointsalong a line passing through the geometric centers of said second targetareas.

5. The arrangement in accordance with claim 3 in which said pluralcylindrical lenses are formed on a multielement cylindrical lensletplate.

6. The arrangement in accordance with claim 1 in which each of saidplural cylindrical lenses is configured to reduce a matrix area imagedimension in a direction perpendicular to said columns to the dimension,in the same direction, of a linear array target area; and

said cylindrical focusing lens is configured to reduce a matrix columnimage dimension, in a direction perpendicular to said rows, to thedimension, in the same direction, of a linear array target area.

1. An optical arrangement for reordering a matrix array of rows and columns of light spots into a corresponding linear array of light spots, said arrangement comprising: a light beam directed to any one of a first plurality of target areas arranged in said matrix array of rows and columns, said columns being aligned at a predetermined angle theta other than the perpendicular with respect to said rows; and means, interposed in the path of said beam and following said matrix array, for redirecting said beam from any given one of said first target areas to a corresponding one of an equal number of second nonoverlapping target areas disposed in a linear array, said redirecting means comprising plural cylindrical lenses, each of said lenses being aligned parallel with a different column of said matrix array and being configured to reduce the images of the target areas in the column in a direction perpendicular to said column, and a cyLindrical focusing lens positioned in the path of said beam between said plural cylindrical lenses and said linear array of second target areas, said focusing lens being aligned parallel with respect to said rows of first target areas to reduce the dimensions in a direction perpendicular to said rows of each column of the images of said second target areas and in cooperation with said plural cylindrical lenses to project said images into said linear array of second target areas.
 2. The arrangement in accordance with claim 1 in which said linear array is aligned parallel with the rows of said matrix, and said cylindrical focusing lens and said plural cylindrical lenses are confocal with respect to said second target areas.
 3. The arrangement in accordance with claim 2 in which said first target areas have a substantially round geometry, and said second target areas and the images projected onto said second target areas of said linear array have a substantially round geometry, said images and said second target areas having a diameter reduced by approximately the factor sin theta with respect to the diameter of said first target areas.
 4. The arrangement in accordance with claim 3 in which said first target areas are tangential to one another only at points along lines parallel with said rows and columns and passing through the geometric centers of such target areas, and said second target areas are tangential to one another only at points along a line passing through the geometric centers of said second target areas.
 5. The arrangement in accordance with claim 3 in which said plural cylindrical lenses are formed on a multielement cylindrical lenslet plate.
 6. The arrangement in accordance with claim 1 in which each of said plural cylindrical lenses is configured to reduce a matrix area image dimension in a direction perpendicular to said columns to the dimension, in the same direction, of a linear array target area; and said cylindrical focusing lens is configured to reduce a matrix column image dimension, in a direction perpendicular to said rows, to the dimension, in the same direction, of a linear array target area. 